Jammer Mitigation in Absorptive RIS-Assisted Uplink NOMA

TL;DR

This paper introduces an innovative absorptive reconfigurable intelligent surface (A-RIS) to mitigate jamming in uplink NOMA systems, significantly reducing user transmit power and interference, especially with large jammer and A-RIS configurations.

Contribution

The paper proposes a novel A-RIS design and an iterative optimization algorithm for power and reflection coefficient control in uplink NOMA under jamming conditions.

Findings

A-RIS dramatically reduces user transmit power compared to standard RIS.

The proposed algorithm converges efficiently for large-scale problems.

A-RIS effectively mitigates interference when jammer and A-RIS sizes are comparable.

Abstract

Non-orthogonal multiple access (NOMA) is a promising technology for next-generation wireless communication systems due to its enhanced spectral efficiency. In this paper, we consider an uplink NOMA system operating together with a high-dimensional absorptive reconfigurable intelligent surface (A-RIS). We aim to minimize the total power transmitted by the users in order to meet signal-to-interference-plus-noise constraints at the base station in the presence of a jammer. We propose an iterative algorithm to solve the high-dimensional non-convex optimization problem using linear programming to find the transmit powers and a fractional programming algorithm based on the Dinkelbach algorithm with a sequential convex relaxation procedure to optimize the reflection coefficients. We show that our algorithm converges on large optimization problems, with a jammer comprising as many as $64$ antennas, and an A-RIS with $128$ elements. Our numerical results show that, compared with a standard RIS that reflects all impinging energy, the A-RIS can dramatically reduce the users' required transmit power and successfully mitigate interference from the jammer. The absorption capability of the A-RIS is in particular useful in cases when the number of jammer antennas is of the same order as the number of A-RIS elements.